Here's a quirk of Commodore BASIC for you:
Firstly, type your string as you usually would, then go to the line with your string in and at the end at the last character of it, press SHIFT+INS/DEL for as many characters as you have (in the example, 13). Now press the INS/DEL key up to the closing quotation mark. A reversed T should fill the string to the closing quotation mark.

Printing the string will not show anything (and in the listing it looks like an empty string), but printing it to the length of the original message using the LEFT$ command will show it.

This was a nice trick when I wanted to hide my passwords when I was 10 or 11